I took BitDefender Total Security 2018 for a test run in a Windows 10 x64 CU VM after seeing some posts here and also got the -4 errors.

Longish story short I found that I could stop these errors and prevent the program (in this case firefox) from crashing by blocking the related "BitDefender Active Threat Control Usermode Filter" dll from getting loaded in the sandboxed process.
Adding something like ClosedFilePath=*atcuf*.dll did the trick in my tests and should work across BitDefender builds with different folder structures but carries a small risk of catching a similarly named (but unrelated) dll

wouldn't carry such a risk and it should do the trick across build types [untested].

This method would be slightly better IMO as it blocks access to the involved dll in order to prevent the crash but also allows the other BD dlls to get injected normally so that less 'potential protection' is lost for the sandboxed app(s).

I took BitDefender Total Security 2018 for a test run in a Windows 10 x64 CU VM after seeing some posts here and also got the -4 errors.

Longish story short I found that I could stop these errors and prevent the program (in this case firefox) from crashing by blocking the related "BitDefender Active Threat Control Usermode Filter" dll from getting loaded in the sandboxed process.
Adding something like ClosedFilePath=*atcuf*.dll did the trick in my tests and should work across BitDefender builds with different folder structures but carries a small risk of catching a similarly named (but unrelated) dll

wouldn't carry such a risk and it should do the trick across build types [untested].

This method would be slightly better IMO as it blocks access to the involved dll in order to prevent the crash but also allows the other BD dlls to get injected normally so that less 'potential protection' is lost for the sandboxed app(s).

I have the same BitDefender as you, and same problem. I inserted this line at the end of Global Settings, and now there is no conflict while running with BTS 2018, no error messages appear. I am assuming this is correct, and will not compromise my PC or Browser security?

Btw, will this custom workaround be added or hard coded into v5.21 so that BTS 2018 can work with Sandboxie with no further conflicts?

I have the same BitDefender as you, and same problem. I inserted this line at the end of Global Settings, and now there is no conflict while running with BTS 2018, no error messages appear. I am assuming this is correct, and will not compromise my PC or Browser security?

It will not compromise your PC or general browser security per se as it will only affect applications ran inside sandboxie. Most of the BitDefender protections will still be applied normally, including traditional signature scans and the Active Virus Control Usermode Filtering Library. By denying access to the ATC dll, which is involved in the crash, we have specifically cut out part of the usermode side of BitDefenders ATC Monitoring but just for sandboxed apps. I'm fairly at ease saying you won't be missing out on much in the case of BD ATC, so far as I understand it, because most of its protections are redundant or irrelevant when the application in question is already running inside SBIE IMHO.

After workarounds are reviewed by the devs, they might get added to a future beta / release of Sandboxie.
When that happens, a notification is added to the original posts, and there is also a mention in the build's notes about it.

I took BitDefender Total Security 2018 for a test run in a Windows 10 x64 CU VM after seeing some posts here and also got the -4 errors.

Longish story short I found that I could stop these errors and prevent the program (in this case firefox) from crashing by blocking the related "BitDefender Active Threat Control Usermode Filter" dll from getting loaded in the sandboxed process.
Adding something like ClosedFilePath=*atcuf*.dll did the trick in my tests and should work across BitDefender builds with different folder structures but carries a small risk of catching a similarly named (but unrelated) dll

wouldn't carry such a risk and it should do the trick across build types [untested].

This method would be slightly better IMO as it blocks access to the involved dll in order to prevent the crash but also allows the other BD dlls to get injected normally so that less 'potential protection' is lost for the sandboxed app(s).

BitDefender just updated my Total Security 2017 to 2018 and Sandboxie stopped starting. I tried disabling every BD TS module, but no joy. I un-installed BD TSand now Sandboxie starts and runs again. I will reinstall BD TS and try these fixes. Thanks so much for posting them.